Foil bearings are one attractive bearing option for certain rotating machine applications. A foil bearing typically includes a housing surrounding a rotor shaft and a plurality of thin foil-like plates or layers disposed in a space or gap between the rotor shaft and the bearing housing, and arranged in a circumferential direction in such a manner that each of the foils is attached to the housing in a cantilever fashion with its free end being urged toward the rotor shaft. As the rotor shaft rotates, a fluid such as ambient air is drawn in between the rotor shaft and the foils, creating a fluid film between an outer surface of the rotor shaft and the foils to allow the rotor shaft to rotate with lower friction by essentially floating on the film. Foil bearings that support loads via a fluid film formed as a result of the rotor shaft rotation may be referred to as hydrodynamic foil bearings.
A significant limitation in the application of foil bearings results from a difficulty in determining wear or, more generally, the state of the bearing. Currently, one known indicator of foil bearing wear is the detection of large thermal spikes that develop because of a severe rotor rub against the foil bearing. These transient rubs may occur because of poor fluid film development between the foil and the rotor. Foreign particle ingestion (e.g., sand) or severe radial rotor load transients that exceed the capability of the developed film may also contribute to wear of the foil bearing.
Various sensing devices are known and are generally in use. For example, thermocouples are used for measuring the temperature in components of a device, such as exhaust systems, combustors, turbomachineries, and so forth. In certain other instances, sensing systems such as strain gages are employed to detect physical parameters such as strain in an infrastructure. However, such conventional sensing devices are limited by the operational conditions in which they may be employed. For example, conventional sensing devices are often limited to relatively mild temperature conditions and, as such, limited operational temperature ranges. In other words such conventional devices are not suitable for monitoring foil bearings operating at higher temperature and pressure conditions. Moreover, most sensing devices are simply unsuited to the fine placement that would be needed in a foil bearing application to avoid disturbing the bearing operation. In any event, current applications for foil bearings do not actively monitor bearing conditions with any of these conventional techniques.
There is a need for a device and method that is employed to effectively detect multiple parameters of a foil bearing provided in a machine, for example, in a rotary machine.